Anion Gap Calculator
Use this anion gap calculator to find your serum anion gap from basic metabolic panel values, a screening step for metabolic acidosis.
Updated September 18, 2026
Calculated instantly in your browser — nothing is sent to or stored on our servers.
Medical Disclaimer: This calculator provides a general estimate based on established research and is for educational purposes only, not a substitute for medical advice. Individual results can vary based on health conditions, so consult a qualified healthcare professional or registered dietitian before making significant changes to your diet, exercise, or health routine. Read our full Medical Disclaimer.
How Anion Gap Is Calculated
Blood contains a mix of positively and negatively charged particles that must balance overall, but routine lab panels only measure some of them directly. The anion gap is a calculated stand-in for the unmeasured anions, mostly proteins, phosphates, and sulfates, and a gap outside the expected range is one of the first clues used to narrow down the cause of a metabolic acidosis¹.
What This Calculator Measures
This calculates the anion gap from your basic metabolic panel values, and optionally corrects it for albumin. It's a screening calculation used to help categorize the cause of a metabolic acidosis, not a diagnosis on its own.
The Formula
Anion gap = Sodium − (Chloride + Bicarbonate)
Some labs instead use Anion gap = Sodium + Potassium − (Chloride + Bicarbonate). Neither is universally "the" correct version, this calculator states clearly which formula was used rather than presenting one as the only correct number.
Albumin-corrected anion gap = Anion gap + 2.5 × (4.0 − measured albumin), since low albumin is itself an unmeasured anion, and low albumin can mask what would otherwise be an elevated gap².
How This Calculator Computes Your Result
Enter sodium, chloride, and bicarbonate, plus potassium if you want the potassium-inclusive version. If you enter albumin, we also show the albumin-corrected gap alongside the standard one.
Why the Reference Range Has Shifted Over Time
Reference ranges for the anion gap aren't fixed the way some lab values are. Older textbooks and teaching materials commonly cite a wider range, roughly 8 to 16 mEq/L, reflecting the older lab methods (like flame photometry) that were standard when the anion gap concept became widely used.
Many modern labs, using newer ion-selective electrode methods, now report a narrower range, often closer to 3 to 11 mEq/L. This is a genuine methodological shift, not just noise, which is why comparing your result to your own lab's reported reference range matters more than comparing it to a single fixed number quoted online.
A Note on Accuracy
Reference ranges have shifted over recent decades with changes in laboratory measurement technique. Older textbooks cite a wider normal range than many modern labs now report, check your own lab's reported range rather than a single fixed number.
Frequently Asked Questions
What is the anion gap used for?
It's a standard screening step for identifying the cause of a metabolic acidosis, calculated from sodium, chloride, and bicarbonate on a basic metabolic panel¹.
Should potassium be included in the formula?
Some labs use Na − (Cl + HCO3), others use Na + K − (Cl + HCO3). Neither is universally "the" correct formula, this calculator states which version it used clearly.
What is the albumin-corrected anion gap?
Low albumin can make the anion gap look artificially normal, since albumin is itself an unmeasured anion. The correction adds 2.5 × (4.0 − measured albumin) to account for this².
Is a normal or elevated anion gap diagnostic on its own?
No. This is a screening calculation, an elevated or normal gap both require clinical correlation, not a standalone conclusion.
Sources
Clinical Use of the Anion Gap, Emmett & Narins, Medicine (Baltimore), 1977
Anion Gap and Hypoalbuminemia, Figge et al., Critical Care Medicine, 1998
Anion Gap Calculator
Use this anion gap calculator to find your serum anion gap from basic metabolic panel values, a screening step for metabolic acidosis.
Updated September 18, 2026
Calculated instantly in your browser — nothing is sent to or stored on our servers.
Medical Disclaimer: This calculator provides a general estimate based on established research and is for educational purposes only, not a substitute for medical advice. Individual results can vary based on health conditions, so consult a qualified healthcare professional or registered dietitian before making significant changes to your diet, exercise, or health routine. Read our full Medical Disclaimer.
How Anion Gap Is Calculated
Blood contains a mix of positively and negatively charged particles that must balance overall, but routine lab panels only measure some of them directly. The anion gap is a calculated stand-in for the unmeasured anions, mostly proteins, phosphates, and sulfates, and a gap outside the expected range is one of the first clues used to narrow down the cause of a metabolic acidosis¹.
What This Calculator Measures
This calculates the anion gap from your basic metabolic panel values, and optionally corrects it for albumin. It's a screening calculation used to help categorize the cause of a metabolic acidosis, not a diagnosis on its own.
The Formula
Anion gap = Sodium − (Chloride + Bicarbonate)
Some labs instead use Anion gap = Sodium + Potassium − (Chloride + Bicarbonate). Neither is universally "the" correct version, this calculator states clearly which formula was used rather than presenting one as the only correct number.
Albumin-corrected anion gap = Anion gap + 2.5 × (4.0 − measured albumin), since low albumin is itself an unmeasured anion, and low albumin can mask what would otherwise be an elevated gap².
How This Calculator Computes Your Result
Enter sodium, chloride, and bicarbonate, plus potassium if you want the potassium-inclusive version. If you enter albumin, we also show the albumin-corrected gap alongside the standard one.
Why the Reference Range Has Shifted Over Time
Reference ranges for the anion gap aren't fixed the way some lab values are. Older textbooks and teaching materials commonly cite a wider range, roughly 8 to 16 mEq/L, reflecting the older lab methods (like flame photometry) that were standard when the anion gap concept became widely used.
Many modern labs, using newer ion-selective electrode methods, now report a narrower range, often closer to 3 to 11 mEq/L. This is a genuine methodological shift, not just noise, which is why comparing your result to your own lab's reported reference range matters more than comparing it to a single fixed number quoted online.
A Note on Accuracy
Reference ranges have shifted over recent decades with changes in laboratory measurement technique. Older textbooks cite a wider normal range than many modern labs now report, check your own lab's reported range rather than a single fixed number.
Frequently Asked Questions
What is the anion gap used for?
It's a standard screening step for identifying the cause of a metabolic acidosis, calculated from sodium, chloride, and bicarbonate on a basic metabolic panel¹.
Should potassium be included in the formula?
Some labs use Na − (Cl + HCO3), others use Na + K − (Cl + HCO3). Neither is universally "the" correct formula, this calculator states which version it used clearly.
What is the albumin-corrected anion gap?
Low albumin can make the anion gap look artificially normal, since albumin is itself an unmeasured anion. The correction adds 2.5 × (4.0 − measured albumin) to account for this².
Is a normal or elevated anion gap diagnostic on its own?
No. This is a screening calculation, an elevated or normal gap both require clinical correlation, not a standalone conclusion.
Sources
Clinical Use of the Anion Gap, Emmett & Narins, Medicine (Baltimore), 1977
Anion Gap and Hypoalbuminemia, Figge et al., Critical Care Medicine, 1998
Anion Gap Calculator
Use this anion gap calculator to find your serum anion gap from basic metabolic panel values, a screening step for metabolic acidosis.
Updated September 18, 2026
Calculated instantly in your browser — nothing is sent to or stored on our servers.
Medical Disclaimer: This calculator provides a general estimate based on established research and is for educational purposes only, not a substitute for medical advice. Individual results can vary based on health conditions, so consult a qualified healthcare professional or registered dietitian before making significant changes to your diet, exercise, or health routine. Read our full Medical Disclaimer.
How Anion Gap Is Calculated
Blood contains a mix of positively and negatively charged particles that must balance overall, but routine lab panels only measure some of them directly. The anion gap is a calculated stand-in for the unmeasured anions, mostly proteins, phosphates, and sulfates, and a gap outside the expected range is one of the first clues used to narrow down the cause of a metabolic acidosis¹.
What This Calculator Measures
This calculates the anion gap from your basic metabolic panel values, and optionally corrects it for albumin. It's a screening calculation used to help categorize the cause of a metabolic acidosis, not a diagnosis on its own.
The Formula
Anion gap = Sodium − (Chloride + Bicarbonate)
Some labs instead use Anion gap = Sodium + Potassium − (Chloride + Bicarbonate). Neither is universally "the" correct version, this calculator states clearly which formula was used rather than presenting one as the only correct number.
Albumin-corrected anion gap = Anion gap + 2.5 × (4.0 − measured albumin), since low albumin is itself an unmeasured anion, and low albumin can mask what would otherwise be an elevated gap².
How This Calculator Computes Your Result
Enter sodium, chloride, and bicarbonate, plus potassium if you want the potassium-inclusive version. If you enter albumin, we also show the albumin-corrected gap alongside the standard one.
Why the Reference Range Has Shifted Over Time
Reference ranges for the anion gap aren't fixed the way some lab values are. Older textbooks and teaching materials commonly cite a wider range, roughly 8 to 16 mEq/L, reflecting the older lab methods (like flame photometry) that were standard when the anion gap concept became widely used.
Many modern labs, using newer ion-selective electrode methods, now report a narrower range, often closer to 3 to 11 mEq/L. This is a genuine methodological shift, not just noise, which is why comparing your result to your own lab's reported reference range matters more than comparing it to a single fixed number quoted online.
A Note on Accuracy
Reference ranges have shifted over recent decades with changes in laboratory measurement technique. Older textbooks cite a wider normal range than many modern labs now report, check your own lab's reported range rather than a single fixed number.
Frequently Asked Questions
What is the anion gap used for?
It's a standard screening step for identifying the cause of a metabolic acidosis, calculated from sodium, chloride, and bicarbonate on a basic metabolic panel¹.
Should potassium be included in the formula?
Some labs use Na − (Cl + HCO3), others use Na + K − (Cl + HCO3). Neither is universally "the" correct formula, this calculator states which version it used clearly.
What is the albumin-corrected anion gap?
Low albumin can make the anion gap look artificially normal, since albumin is itself an unmeasured anion. The correction adds 2.5 × (4.0 − measured albumin) to account for this².
Is a normal or elevated anion gap diagnostic on its own?
No. This is a screening calculation, an elevated or normal gap both require clinical correlation, not a standalone conclusion.
Sources
Clinical Use of the Anion Gap, Emmett & Narins, Medicine (Baltimore), 1977
Anion Gap and Hypoalbuminemia, Figge et al., Critical Care Medicine, 1998